ARN number

I've been on the phone for many hours with standard bank and they have no idea what an ARN number. The agents are confused and they keep forwarding my calls to different departments who are just as useless. The bank has got terrible customer service, they are slow and to be honest they don't care. They say they want proof from the Broker I used but they gave me an ARN number to show that the transaction has gone through, but Standard Bank do not know what this is. I've always had issues with standard bank and I think I've had enough. I'm on the verge of losing a vast amount of money but no one at the bank cares.